Method of manufacturing a tubular printed circuit armature

ABSTRACT

Tubular high torque - low inertia printed circuit armatures are manufactured from two flexible circuit cards. Each card is comprised of a layer of conductive metal laminated to a layer of insulation. The layer of insulation is patterned to expose a pair of spaced parallel bands of metal, on the insulation side of each card. These spaced bands form the circuit interconnecting tabs of the metal winding conductors which extend into the spaced bands. The abutting surfaces of the two cards are coated with an adhesive which will bond the cards together under a heat and pressure environment. The cards are loosely rolled about a low or zero temperature coefficient mandrel, with the interconnecting tabs of one card in registry with the interconnecting tabs of the other card, and with the cards axially overlapping one another at the sides which form the axial seam of the tubular armature. The diameter of the mandrel accurately establishes the inner diameter of the finished armature. The mandrel and encircling cards are placed in an inflatable oven. This oven is formed by a rubber sleeve or tube which carries an integral heater and a temperature sensor. The oven is pressurized to thereby force the two cards down onto the mandrel. The heater is energized and a servocontrolled temperature is maintained for a given time period. The resulting tube is removed from the mandrel, and the tabs are electrically connected to form the armature winding.

United States Patent [191 Herr-on METHOD OF MANUFACTURING A TUBULAR PRINTED CIRCUIT ARMATURE [75] Inventor: Christopher C. Herron, Boulder,

[73] Assignee: International Business Machines Corporation, Armonk, N.Y.

[22] Filed: June 12,1972 [21] Appl. No.: 261,893

Primary Examiner-Charles W. Lanham Assistant Examiner-Carl E. Hall Attorney-Francis A. Sirr et al.

[57] ABSTRACT Tubular high torque low inertia printed circuit ar- PRESSURE CONTROLLER ALIGNMENT PIN 22 MANOREL Oct. 9, 1973 matures are manufactured from two flexible circuit cards. Each card is comprised of a layer of conductive metal laminated to a layer of insulation. The layer of insulation is patterned to expose a pair of spaced parallel bands of metal, on the insulation side of each card. These spaced bands form the circuit interconnecting tabs of the metal winding conductors which extend into the spaced bands. The abutting surfaces of the two cards are coated with an adhesive which will bond the cards together under a heat and pressure environment. The cards are loosely rolled about a low or zero temperature coefficient mandrel, with the interconnecting tabs of one card in registry with the interconnecting tabs of the other card, and with the cards axially overlapping one another at the sides which form the axial seam of the tubular armature. The diameter of the mandrel accurately establishes the inner diameter of the finished armature. The mandrel and encircling cards are placed in an inflatable oven. This oven is formed by a rubber sleeve or tube which carries an integral heater and a temperature sensor. The oven is pressurized to thereby force the two cards down onto the mandrel. The heater is energized and a servo-controlled temperature is maintained for a given time period. The resulting tube is removed from the mandrel, and the tabs are electrically connected to form the armature winding.

12 Claims, 4 Drawing Figures PRESSURE SOURCE 80 HOUSING RUBBER HEATING BLADDER 64 PAIENIED 91975 35163551 saw 10F 2 FIG. I

PAIENTEO 91973 3.763.551

SHEET 2 OF 2 COPPER SLEEVE 56 TYPICAL P ETOHEO OONDUOTO 52 OUTER FIBERGLASS LAYER 53 INNER COPPER LAYER 5O PRESSURE CONTROLLER PRESSURE 80 SOURCE METHOD OF MANUFACTURING A TUBULAR PRINTED CIRCUIT ARMATURE BACKGROUND AND SUMMARY OF THE INVENTION The present invention relates to the general field of metal working, and specifically to the field of processes for mechanically manufacturing the rotor of a dynamoelectric machine, more specifically, a tubular printed circuit armature for use in a high torque low inertia direct current motor of the type used to drive the capstan of a magnetic tape transport. A motor of this type is shown in U. S. Pat. No. 3,490,672 to G. A. Fisher and H. E. Van Winkle.

Printed circuit armatures typically comprise an electrically nonconductive, insulating, support on which a conductive armature winding is formed. The prior art teaches three general methods of forming this winding. In one method, the winding is stamped out of a metal sheet and then attached to the insulating support. In another method, the winding is photoetched after the metal layer has been attached to the carrier. Another method forms the winding from a length of wire. These prior art armatures are of the disk, cone, basket, or tube type.

The present invention relates to a method of making a cone, basket, or tube type armature by the use of pneumatic clamping and heat curing techniques, and the term tube will be used generically hereafter.

Prior art tubular armatures have been manufactured from flat metal/insulator laminate cards. A portion of the armatures winding is first formed in each metal layer, while the cards are in the flat state. The cards are then loosely formed into two tubes. The two tubes are assembled into a unitary tube, as by wrapping with thread, and adhesive is then forced between the tubes.

US. Pat. No. 3,650,021 to K. N. Karol discloses a method for manufacturing a tubular printed circuit armature wherein two metal/insulator laminate cards are formed into a tubular armature by a differential expansion fixture. This fixture is temperature activated and includes a high-expansion central mandrel which operates to force the cards outwardly against the tubular surface of a dimensionally stable outer shell whose inner diameter accurately controls the armature s outer diameter. While this method is a considerable advance over the prior art, this methods pressure and temperature cannot be independently controlled. These method parameters are rendered interdependent by virtue of the operating principle of the fixture. Thus, each fixture is designed with a particular pressure and temperature in mind. Since the stable reference member is the outer shell, all manufacturing tolerances in the thickness of the cards, etc., are reflected to the armatures inner diameter.

The present invention includes some of the steps of A the above-mentioned Karol method, such as preparing two laminated metal/insulator cards having spaced sur faces of clean, exposed metal on the insulator side of the cards, and coating at least one side of one card with a temperature activated adhesive. However, the present invention facilitates independent control and variation of the pressure and temperature. Additionally, the

'present invention accurately controls the armatures inner diameter.

The laminating fixture used in practicing the present invention includes a pneumatic tubular shaped oven whose tubular opening is formed by a rubber-like sleeve. This sleeve is one wall of a closed chamber which can be pressurized to any selected pressure or pressuretime profile, thus providing independent control of the lamination pressure. The sleeve carries an integral electrical heater about its 360 circumference. This heater can be energized and servo-controlled to produce any selected temperature or temperature-time profile, thus providing independent control of the lamination temperature. The heater carries a temperature sensor integrally therewith to facilitate servo-control of the temperature to a command temperature.

This lamination fixture preferably cooperates with a substantially zero temperature. coefficient mandrel, for example, ceramic, about which the cards are wrapped, prior to insertion into the sleeve of the abovementioned oven. With this type mandrel, manufacturing tolerances, such as variation in thickness of the card material, arereflected to the outside diameter of the armature and the armatures inner diameter is accurately established by the diameter of the dimensionally stable mandrel.

This mandrel may include an axially disposed central opening for the purpose of admitting heating and/or cooling medium.

The method of the present invention provides a unique means whereby the above-mentioned cards are mechanically forced together and the intermediate adhesive set thermally, and wherein both of these phenomena are independently controlled.

Additional steps of the present invention include, without limitation, the step of wrapping a metal-sleeve about the cards, prior to insertion into the oven, this sleeve performing the function of preventing localized pressure and/or temperature during lamination; and the step of passing heating and/or cooling fluid through the center of the mandrel.

The foregoing and other features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the present invention, as illustrated in the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a view of two flat laminated cards which may be used in the practice of the present invention to make one tubular armature, showing the winding conductors, the spaced metal surfaces which constitute the circuit interconnect tabs, and the manufacturing holes which facilitate card alignment on the mandrel,

FIG. 2 is a view of another form of flat laminated card, two of these cards facilitating the manufacture of two armatures in a single method cycle of the present invention,

FIG. 3 shows two cards of the form shown in FIG. 2, wrapped about the mandrel, with the metal sleeve positioned over the outer card, and with parts thereof broken away to show the circumferential positioning of the three axial seams, and

FIG. 4 is a view, partially broken away, of the tubular pneumatic oven.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. ll, two or more flat laminated cards, of the type used to make an armature, are prepared with a solid sheet of conductive metal 10, for example copper or aluminum, laminated to a layer of insulation 11, for example fully cured epoxy-fiberglass. By way of example, metal or copper layer 10 may have a thickness of mils and insulator or fiberglass layer 11 may have a thickness of 4 mils. At the portions 17 and 18 of the cards, which will eventually be the copper interconnecting tabs for the inner and outer armature winding conductors, the layer of fiberglass is removed, exposing spaced surfaces of copper on the fiberglass side of each card. FIG. 1 shows two cards which are used to form the inner and outer conductor surfaces, respectively, of a single tubular armature. As an alternative, the two cards may be of the typeshown in FIG. 2. The single card of FIG. 2 corresponds to the upper card of FIG. I. This card, in combination with a second card having the general characteristics of the lower card of FIG. I, facilitates the making of two armatures with a single method cycle of the present invention.

Each card, of the type shown in FIGS. 1 or 2, is coated with a photoresist and subjected to photoetching techniques on the copper side of the card, to produce one card having the outer winding conductors and one card having the outer winding conductors. An individual conductor consists of a relatively long axially extending portion 14 having oppositely inclined crossover portions 15 and 16 at each end. The crossover portions terminate in short axially extending interconnecting tabs 17 and 18. These tabs are the above-mentioned interconnecting tabs which will connect the inner conductors to the outer conductors. The tabs terminate in a copper selvage surface 19. After the circuit is formed, the card is cleaned to remove photoresist, grease, and the like.

The cards are now masked on the fiberglass side, to cover selvage portions 19, including interconnecting tabs 17 and I8. The unmasked fiberglass layer of one or both cards is then coated with a thermal activated or setting adhesive. The term thermal activated or setting adhesive as used herein is meant to encompass a means for later bonding the cards together by means of elevated temperature. For example, a heat reflowable thermoplastic adhesive may be used, or the cards may be coated with epoxy which is thenB-staged.

The cards are then cut, as best shown in FIG. 1, such that each axially extending edge of the card is bordered by an individual winding conductor l7, l5, l4, l6, 18. The two ends of the cards (FIG. 1) and the two ends and middle of the cards (FIG. 2) include the interconnecting tabs 17, 18. These tabs terminate in selvage 19 which will eventually be discarded. Positioning indicia in the form of manufacturing holes 20 are formed to extend completely through the card, in this selvage area. These openings are used to position the two cards in proper alignment on the mandrel of FIG. 3, after they have been preformed to a generally open tubular shape.

The two preformed cards are loosely assembled on cylindrical mandrel 21. This mandrel is preferably formed of a material having a substantially zero temperature coefficient of expansion, for example, ceramic. The cards are positioned with the adhesive coated fiberglass surfaces abutting.

The use of a dimensionally stable mandrel accurately controls the armature inner diameter. This feature is of particular advantage when it is desired to build a high torque low inertia motor of the type shown in abovementioned U. S. Pat. No. 3,490,672 wherein it is necessary to establish a minimum air gap between the armatures inner surface and an adjacent stationary flux return path member.

The mandrel includes positioning indicia in the form of removable locating pins 22. Two such pins are used for the cards of FIG. I, while three pins are used for the cards of FIG. 2, the center pin thereof having flat ends which are substantially flush with the cylindrical surface of the outer metal sleeve. The cards are assembled on the mandrel with the card holes 20 mating with the mandrels locating pins 22.

Mandrel 21, in a specific embodiment, was constructed as a cylinder having a central opening 23. This opening can be connected to a source of heating fluid during the subsequent heat cycle, and to a source of cooling fluid during the subsequent cooling cycle, to be described.

In FIG. 3, two cards of the type shown in FIG. 2 have been preformed into a generally cylindrical shape and have been loosely placed on mandrel 21. These cards have been broken away to show the innermost copper surface 50. The two side edges of this inner card abut at 51 to form an axial seam. Insulator layer 52 of the innermost card abuts insulator layer 53 of the outer card. The interface between these two insulator layers includes the thermal setting adhesive, above mentioned. The outer surface of the armature consists of copper layer 54. The side edges of the outer card abut to form axial seam 55. As is apparent, the two cards are aligned by manufacturing holes 20, not shown in FIG. 3, such that the two card scams 5] and 55 are not in radial alignment, but rather are circumferentially displaced to form a strong overlap scam in the armature tube.

The outermost layer of the composite tubular structure of FIG. 3 is thin copper sleeve 56. This sleeve has the same flat shape as outer card 53, 54 (see FIG. 2) and its axially extending seam 57 is placed in alignment with outer card seam 55. This alignment is assured by manufacturing holes 20, not shown, which are formed in sleeve 56. This sleeve functions to insure uniform pressure and heat transfer to the underlying cards.

The mandrel and cards, assembled into a composite tubular structure as shown in FIG. 3, are placed in pneumatic-electric oven 58, as shown in FIG. 4.

Oven 58 includes a closed, tubular-shaped chamber 59. This chamber is formed by a solid metal base 60, a solid, generally U-shape, metal wall 61 and two metal end plates 62 and 63. Each end plate includes an axially aligned opening, somewhat larger in diameter than the composite mandrel structure of FIG. 3.

Closed chamber 59 is completed by a tubular shaped,

. flexible, rubber-like electric heater 64. The central opening of this heater is of a diameter somewhat larger than the composite mandrel structure of FIG. 3 and is aligned with the openings in end plates 62 and 63. The heater includes, at each end, an annular flange 65 which is sealed to the inner surface of end plates 62 and 63, respectively.

The electrical heater portion of member 64 is not shown in FIG. 4. As those skilled in the art will readily understand, member 64 includes an integral electrical heater whose wires are buried within the flexible surface of member 64. This heater is physically oriented therein such that the total length and circumference of member 64 provides uniform heat transfer to the underlying tubular oven opening in which the composite mandrel structure of FIG. 3 is placed. Electrical connections 70 supply electrical energy to the heater. This electrical energy is servo-controlled by controller 71. Controller 71 receives the output of a temperature sensor, not shown, as a control input. The temperature sensor is carried integrally by the tubular wall of heater 64. Controller 71 includes a control point selecting adjustment 72 and a meter readout 73 of the actual heater temperature. The controller compares this actual temperature to the set point temperature and variably controls the transfer of electrical energy from source 74 to heater 64. This simple showing of a means for servocontrolling temperature does not preclude the use of a more complicated means which provides a variable temperature-time profile.

Oven 58 also includes a pneumatic coupling which connects chamber 59 to pressure source 80, for example, a source of compressed air. The pressure maintained within chamber 59 is variably controlled by pressure controller 81. Controller 81 includes means to select a desired pressure to be supplied to chamber 59, as well as means to connect chamber 59 to ambient or atmospheric pressure, to thereby facilitate insertion and removal of the composite mandrel structure of FIG. 3. This means for controlling the pressure within chamber 59 is meant to include a means for providing a variable pressure-time profile.

As can be seen in FIG. 4, the length of oven 58 is less than the length of the composite mandrel of FIG. 3. Preferably, the length 'of oven 58 is such that when the composite mandrel of FIG. 3 is centered in the oven, all portions of the cards, with the exception of the interconnect tabs l7 and 18 at the extreme ends of the cards, are under an elevated pressure and temperature environment. l

The composite mandrel of FIG. 3 is placed in the oven, as shown in FIG. 4, and is subjected to an elevated pressure by pressurization of chamber 59. This pressure causes heater 64 to move radially inward to force sleeve 56 and the two cards down onto the dimensionally stable outer surface of mandrel 21, bringing the seams 51, 55, and 57 (FIG. 3) into abutting alignment. The specific pressure selected is a function of parameters such as the card materials and the adhesivecharacteristics. A particular advantage realized by this construction is that the pressure parameter can be varied at will to determine the optimum pressure for particular armature materials and thicknesses.

After oven 58 is pressurized, controller 71 becomes operative, either manually or by means of a pressure sensor within chamber 59, not shown. Heater 64 heats the composite mandrel structure to a control temperature. This temperature may, if desired, include a variable temperature-time profile which is selected in accordance with the particular materials being used to form the armature. Here again, the temperature parameter is independently variable and facilitates modification of this method parameter to investigate the effect of such modification.

This elevated temperature activates the adhesive between insulator layers 52 and 53, FIG. 3. A rigid tube is thus formed from the two cards 50, 52 and 53, 54.

The specific temperature, pressure and time period of the method is matched to the characteristics of the armature materials. For example, for 1.3 inches diameter and a 4-inch long armature whose cards have the metal and insulator layer thickness above described,

the pressure is elevated from ambient pressure to psi, the temperature is elevated from ambient temperature to 350 F, and the pressure and temperature environment are maintained for 20 minutes. The inward compression of heater 64 forces the cards together to insure good mechanical contact between the cards, while the elevated temperature of heater 64 activates the adhesive such that a structurally sound tube results. Sleeve 56 insures that both pressure and temperature are uniformly distributed to the underlying cards. The axial seam 57 in sleeve 56 is placed in alignment with the seam 55 of the outer card (FIG. 3) to insure that sleeve 56 does not interfere with movement of the underlying card as the overlapped axial seam is formed between the two cards.

After a time period of the pressure temperature environment, the oven is allowed to cool, either to ambient temperature or to a somewhat higher than ambient temperature, such as 100 F. Chamber 59 is now restored to ambient pressure and the composite mandrel is removed from the oven. Pins 22 and sleeve 56 are removed. The now-solid tube which has been formed from the two cards 50, 52 and 53, 54 is forced off mandrel 21. For example, the composite mandrel may be placed in a pneumatic chuck which resiliently holds the outer surface 54 of the armature, and a hydraulic ram may be used to slowly force mandrel 21 out of the center of the armature.

Equivalent steps to these above described will be apparent to those skilled in the art. For example, the term photoetching technique suggests other known means of forming a conductor pattern out of solid sheet of metal, as by stamping, cutting or scribing. It is also within the teachings of this invention to position the inner card such that its conductors abut the insulation layer of the outer card and are thus buried between the two cards. In this latter case, the resulting tubular armature will have an insulator surface exposed as its inner surface.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

11. The method of manufacturing a tubular printed circuit armature for an electrical machine, comprising the steps of:

preparing at least two laminated cards having a flexible layer of electrically conductive metal bonded to a patterned flexible layer of electrical insulation, the pattern in said layer of insulation providing spaced surfaces of exposed metal layer on the insulation side of the cards,

coating at least one side of one card with a layer of thermal activated adhesive, such that said spaced surfaces of said metal layer remain uncoated, placing said cards into a pneumatic-eletric oven having an openend, tubular shaped flexible wall- /heater, with said cards loosely surrounding a tubular shaped manufacturing mandrel having a substantially zero temperature coefficient of expansion, such that (a) said one side of said one card is adjacent the other card, (b) said spaced surfaces of said metal layer in each of said cards are in alignment, and (c) said cards overlap to form a double card thickness at the central portion and a single card thickness at each end portion, the end portions then overlapping to form an axial seam in the tube which is thereby formed about said mandrel,

pressurizing said oven to force said cards mechanically together and radially inward onto the underlying surface of said mandrel,

energizing said oven to activate said adhesive,

subsequently de-energizing and depressurizing said oven, and

thereafter removing said mandrel from said oven and mechanically forcing said cards off one end of said mandrel.

2. The method as defined in claim 1 wherein said mandrel includes an axial opening, and including the step of admitting a heating and/or cooling medium to the inner portion of said mandrel substantially coincident with energization and/or subsequent deenergization of said oven.

3. The method as defined in claim 1 wherein said wall/heater includes an integral electrical heater about the circumference of said cards and an integral temperature sensor, and including the step of servocontrolling the temperature of said wall/heater.

4. The method as defined in claim 3 including the step of placing an axially split metal sleeve between the outer one of said cards and said wall/heater.

5. The method as defined in claim 4 wherein said metal sleeve is identical in shape to the outer of said two cards, and wherein said step of placing said metal sleeve over said outer card includes the step of aligning the axial seam of said sleeve with the axial seam of said outer card.

6. The method as defined in claim 1 wherein, prior to the step of coating with said adhesive, each of said cards are processed to produce a plurality of individual armature conductors in the metal layer, each of said individual conductors terminating in said spaced surfaces of said metal layer, and wherein said cards are placed on said mandrel in a manner such that the terminating portion of a conductor in one card overlaps the terminating portion of a conductor of the other card.

7. The method as defined in claim 6 wherein said flexible wall/heater is constructed and arranged such that the step of pressurizing said chamber does not force said terminating portions of said conductors together.

8. The method as defined in claim 6 wherein, after said mandrel is removed from said shell and said cards are forced off said mandrel, said overlapping terminating portions of said conductors are electrically interconnected.

9. The method as defined in claim 8 wherein said cards include selvage material at the end of each card adjacent said spaced surfaces of said metal layer, and including the step of forming manufacturing holes in said selvage material, and aligning said manufacturing holes with indicia carried by said mandrel.

10. The method as defined in claim 9 wherein said wall/heater includes an integral electrical heater disposed about the total circumference of said cards, and also includes an integral temperature sensor, and including the step of servo-controlling the temperature of said wall/heater.

11. The method as defined in claim 10 including the step of placing a metal sleeve, having the same shape as the outer card, between said outer card and said wall/heater to ensure uniform distribution of pressure and heat to said cards, and the step of aligning the axial seam of said sleeve with the axial seam of said outer card.

12. The method as defined in claim 11 wherein said mandrel includes an axial opening, and including the step of admitting a heating and/or a cooling medium to the inner portion of said mandrel substantially coincident with energization and/or subsequent deenergization of said oven. 

1. The method of manufacturing a tubular printed circuit armature for an electrical machine, comprising the steps of: preparing at least two laminated cards having a flexible layer of electrically conductive metal bonded to a patterned flexible layer of electrical insulation, the pattern in said layer of insulation providing spaced surfaces of exposed metal layer on the insulation side of the cards, coating at least one side of one card with a layer of thermal activated adhesive, such that said spaced surfaces of said metal layer remain uncoated, placing said cards into a pneumatic-electric oven having an open-end, tubular shaped flexible wall/heater, with said cards loosely surrounding a tubular shaped manufacturing mandrel having a substantially zero temperature coefficient of expansion, such that (a) said one side of said one card is adjacent the other card, (b) said spaced surfaces of said metal layer in each of said cards are in alignment, and (c) said cards overlap to form a double card thickness at the central portion and a single card thickness at each end portion, the end portions then overlapping to form an axial seam in the tube which is thereby formed about said mandrel, pressurizing said oven to force said cards mechanically together and radially inward onto the underlying surface of said mandrel, energizing said oven to activate said adhesive, subsequently de-energizing and depressurizing said oven, and thereafter removing said mandrel from said oven and mechanically forcing said cards off one end of said mandrel.
 2. The method as defined in claim 1 wherein said mandrel includes an axial opening, and including the step of admitting a heating and/or cooling medium to the inner portion of said mandrel substantially coincident with energization and/or subsequent deenergization of said oven.
 3. The method as defined in claim 1 wherein said wall/heater includes an integral electrical heater about the circumference of said cards and an integral temperature sensor, and including the step of servo-controlling the temperature of said wall/heater.
 4. The method as defined in claim 3 including the step of placing an axially split metal sleeve between the outer one of said cards and said wall/heater.
 5. The method as defined in claim 4 wherein said metal sleeve is identical in shape to the outer of said two cards, and wherein said step of placing said metal sleeve over said outer card includes the step of aligning the axial seam of said sleeve with the axial seam of said outeR card.
 6. The method as defined in claim 1 wherein, prior to the step of coating with said adhesive, each of said cards are processed to produce a plurality of individual armature conductors in the metal layer, each of said individual conductors terminating in said spaced surfaces of said metal layer, and wherein said cards are placed on said mandrel in a manner such that the terminating portion of a conductor in one card overlaps the terminating portion of a conductor of the other card.
 7. The method as defined in claim 6 wherein said flexible wall/heater is constructed and arranged such that the step of pressurizing said chamber does not force said terminating portions of said conductors together.
 8. The method as defined in claim 6 wherein, after said mandrel is removed from said shell and said cards are forced off said mandrel, said overlapping terminating portions of said conductors are electrically interconnected.
 9. The method as defined in claim 8 wherein said cards include selvage material at the end of each card adjacent said spaced surfaces of said metal layer, and including the step of forming manufacturing holes in said selvage material, and aligning said manufacturing holes with indicia carried by said mandrel.
 10. The method as defined in claim 9 wherein said wall/heater includes an integral electrical heater disposed about the total circumference of said cards, and also includes an integral temperature sensor, and including the step of servo-controlling the temperature of said wall/heater.
 11. The method as defined in claim 10 including the step of placing a metal sleeve, having the same shape as the outer card, between said outer card and said wall/heater to ensure uniform distribution of pressure and heat to said cards, and the step of aligning the axial seam of said sleeve with the axial seam of said outer card.
 12. The method as defined in claim 11 wherein said mandrel includes an axial opening, and including the step of admitting a heating and/or a cooling medium to the inner portion of said mandrel substantially coincident with energization and/or subsequent de-energization of said oven. 